水-岩作用下单裂隙灰岩渗流特性演化规律研究

针对某水电站地下洞室裂隙灰岩的渗漏问题，现场采集岩样和库水，设计进行了两种方案的水-岩作用试验，历时360 d，其中，方案1在浸泡过程中定期更换浸泡溶液，模拟地下水的长期浸泡和流动更新现象，方案2主要模拟长期浸泡过程。综合水-岩作用下裂隙面微观形貌特征以及浸泡溶液中离子浓度变化，分析水-岩作用下裂隙灰岩的渗流特性变化特征及机制。研究结果表明：在浸泡过程中，单裂隙灰岩的渗透系数呈“先快后慢”的增大趋势，浸泡360 d后，2.5、3.0、3.5、4.0 MPa等4种侧向应力在两种方案下单裂隙灰岩的渗透系数分别增大了729.90%～384.17%、549.04%～297.45%，侧向应力越小，裂隙岩样的渗透系数增大趋势越明显，增长趋势分别在120 d和90 d后趋于稳定。比较而言，方案1裂隙灰岩的渗透系数增长速率和幅度明显较大，为方案2的1.34～2.07倍。方案1定期更换浸泡库水，保持了浸泡溶液的不平衡状态，使得岩样与浸泡溶液间形成了较大的浓度梯度，增加了反应化学势，加快了裂隙表面矿物溶解、溶蚀速率，而方案2中，长期浸泡使得溶液中离子浓度逐渐接近平衡状态，导致裂隙面矿物溶解、溶蚀速率明显低于方案1。长期水-岩作用使得裂隙面粗糙度和波动性明显减小，局部坡度和起伏度逐渐减小，整体溶蚀深度逐渐增加，据此，建立了水-岩作用下单裂隙灰岩渗流通道演化模型，在长期水-岩作用下裂隙岩样的渗流通道逐渐向吻合度低、开度大的方向演化，从而导致了裂隙岩样等效水力开度及渗透系数的大幅度增长。相关研究思路和成果为裂隙岩体的水-岩作用模拟提供了较好的参考。

Study on the evolution of seepage characteristics of single-fractured limestone under water-rock interaction

Regarding the leakage of fractured limestone in the underground cavern of a hydropower station, the rock samples and reservoir water were collected on site, and two schemes of water-rock interaction tests which lasted 360 days were carried out. The scheme #1 regularly changed the soaking solution during the soaking process to simulate the long-term immersion and flow renewal phenomenon of groundwater, while the scheme #2 mainly simulates the long-term immersion process. Based on the micro-morphological characteristics of the fracture surface and the changes of ion concentration in soaking solution, the characteristics and mechanism of the seepage characteristics of fractured limestone under water-rock interactions were analyzed. The research results show that in the course of soaking, the permeability coefficient of the single-fractured limestone increases first sharply then gently. After 360 days of soaking, the permeability coefficients of the single-fractured limestone with 2.5 MPa, 3.0 MPa, 3.5 MPa, and 4.0 MPa confining stresses in the two schemes increased by 729.90%~384.17%、549.04%~297.45%, respectively. The smaller the confining stress is, the more obvious the permeability coefficient increases. Moreover, the growth trends of permeability coefficient stabilized after 120 days for scheme #1 and 90 days for scheme #2. In comparison, the permeability coefficient increase rate and amplitude of single-fractured limestone in scheme #1 are significantly higher, which is 1.34~2.07 times that of scheme #2. In scheme #1, the immersion reservoir water was periodically changed to maintain the disproportion of the immersion solution, which resulted in a large concentration gradient between the rock sample and the solution. This concentration gradient increased the reaction chemical potential, and accelerated the rate of mineral dissolution and erosion on fracture surface. In scheme #2, the long-term immersion facilitated the solution ion concentration to approach the equilibrium state gradually, leading to the dissolution and erosion rate of the minerals on fracture surface being significantly lower than that in the scheme #1. Long-term water-rock interaction weakens the roughness and fluctuation of fracture surface significantly accompanied with the progressively decrease of local slope and undulation, and the increase of overall erosion depth. Based on this, a seepage channel evolution model for single-fractured limestone under long-term water-rock interaction is established. The seepage channels of fractured rock samples gradually evolved to the direction of low anastomosis and large opening, which leads to significantly increases of equivalent hydraulic opening and permeability coefficient of fractured rock samples. The ideas and results of this study provide an excellent reference for the simulation of water-rock interaction in fractured rock masses.